Printed circuit boards (PCBs) are generally arranged on flat panels for inspection by automated inspection systems. Reference information regarding spatial coordinates and geometry of features found on the PCB, such as pads, holes and the like, is typically input to the inspection system from a data base of computerized design software used to lay out the PCB. The inspection system senses the coordinates and geometry of the features, such as by optical sensors, and compares the sensed information to that of the data base. In this manner, the system detects which PCBs are acceptable and which have flaws.
In general, a multiplicity of the PCBs to be inspected rest on flat panels with typical dimensions of 18×24 inches. In prior art systems, reference information is generated for an entire panel. Alternatively, reference information may be generated for a single PCB. However, the PCBs must be arranged in orderly columns and rows so that the inspection system can find a reference point for each PCB from which coordinate measurements are made. For example, the lower left corner may be designated (0,0) and all measurements in (x,y) coordinates are based on that origin. Once the reference points for the PCBs have been found, the inspection system can simply inspect all of the PCBs, since they are all identical to each other without generating a reference for the entire panel.
However, prior art inspection systems cannot readily inspect the PCBs if they are not arranged in an orderly fashion or are not identical to each other.